Light sources, in combination with gratings, have been used as means for detecting acoustic waves, angular positions and environmental changes. However, such devices either have a limited dynamic range or low sensitivity. This is because to achieve high sensitivity, grating lines must have been closely spaced so that small motions result in large intensity modulation. However, to achieve wide dynamic range without saturation or fold-over, the grating spacing has had to be quite wide, resulting in low sensitivity.